Reconstruction of a paleotemperature record from 0.3-3.7ka for subtropical South China using lacustrine branched GDGTs from Huguangyan Maar

The concentrations of glycerol dialkyl glycerol tetraethers (GDGTs) in catchment soils, suspended particulate matter (SPM), lake bottom sediments, and sediment cores from Huguangyan Maar, subtropical South China, were investigated. The distribution of isoprenoid GDGTs has GDGT-0/crenachaol>2 and therefore the widely used TEX₈₆ is precluded from being used for the calculation of lake water temperature in this lake. The total concentration of branched GDGTs (br-GDGTs) in the soils, SPM, and lake bottom sediments ranged from 91.3-223.7ng/g, 17.8-41.4ng/L, and 864.2-2008.6ng/g, respectively. The molecular composition of br-GDGTs, MBT values (methylation of br-GDGTs), and CBT values (the cyclization ratio of br-GDGTs) in the catchment soils differ from those in lake materials. This difference indicates that br-GDGTs in the lake are largely produced in situ. Based on the global lake-specific MBT/CBT-MAT (mean air temperature) calibration, the air temperature was reconstructed for lacustrine material in Huguangyan Maar. The estimates fall in the range 23.2-23.8°C, similar to the average value of local MAT for the preceding 45years. The paleotemperature history of Huguangyan Maar was reconstructed using br-GDGTs extracted from a sediment core spanning the period 0.3-3.7ka, and ranged from 24.6 to 26.3°C. The temperature pattern of Huguangyan Maar based on the global lake-specific MBT/CBT-MAT resembles those recorded in East China using numerous indicators. The pattern consists of five cool and four warm periods, including two distinct phases within the Medieval Warm Period (900-1300AD), the coldest temperature in the Little Ice Age (1550-1850AD) and reveals even finer temperature variations than other indicators. This new method based on br-GDGTs, produced in situ in the subtropical lacustrine environment, provides a new sensitive and precise paleotemperature proxy for lacustrine sediments for which other GDGT-based proxies are not applicable.